1. Field of the Invention
This invention relates to sound processing systems and particularly to systems and circuits having a multifunction analog input/output interface for connection to a speaker that handles input, output, and activation functions.
2. Description of Related Art
Semiconductor memory systems for recording and playing back continuous analog signals such as sound signals require input and output interfaces for the analog signals. An input interface receives an input analog signal and converts the input signal into values that can be stored in the memory. An output interface converts values read from the memory back an output analog signal. FIG. 1 shows a block diagram of a semiconductor memory system 100 for recording and playing sounds. System 100 includes a memory array 140 which stores values received from an input interface including a microphone 120, an input amplifier 122, a converter 124, and write circuitry 126. During recording, microphone 120 picks up sounds and generates an analog input signal representing the sounds. Amplifier 122 amplifies the input analog signal. Typically, the maximum level of the input analog signal depends on the sound level at microphone 120, and amplifier 122 includes an automatic gain control (AGC) or automatic level control (ALC) circuit that adjusts amplifier 122 to amplify the input signal to an appropriate level for converter 124. Converter 124 converts the amplified input signal to values that write circuitry 126 stores in memory array 140. The type of converter 124 employed in the input interface depends on memory array 140. For example, if memory array 140 is a digital memory storing one or more bit of information per memory cell, converter 124 samples the level of the amplified input signal to generate a series of samples and converts each sample into a digital value indicating the level of the sample. Write circuitry 126 then writes a series of digital values to memory array 140. Alternatively, if memory array 140 stores analog values in memory cells, converter 124 samples the amplified input signal, and write circuitry 126 writes analog samples from converter 124 in memory array 140.
An analog output interface, which includes read circuitry 136, a converter 134, an output amplifier 132, and a speaker 130, converts the values stored in memory array 140 back into audible sounds. In particular, read circuitry 136 reads a series of sample values (analog or digital values depending on the type of memory array 140), and converter 134 converts the series into a continuous analog signal. Output amplifier 132 amplifies the analog signal from converter 134 to a level appropriate for driving speaker 130. Speaker 130 produces the sound.
Record and playback systems such as memory system 100 have many applications, and in some applications, low system costs are critical to making the systems practical. To reduce cost, memory circuit 110 may be fabricated as an integrated circuit formed on a single die. Such integration of circuits reduces the number of system components which tends to reduce system cost. However, system components such as microphone 120 and speaker 130 are not currently available or practical in forms that are integrable in an integrated circuit. Accordingly, memory circuit 110 needs input/output circuitry and pins for connection to microphone 120 and speaker 130. The needs of the input/output interface thus restrict the pin count and circuit size and can affect system costs. To provide a lower cost system than is currently available, systems and methods for reducing the number of system component and/or integrated circuit pin counts are sought.